In internal combustion engines a high compression ratio influences efficiency of the internal combustion engine in a positive manner. Compression ratio is typically defined as a ratio of an entire cylinder volume before compression to the remaining cylinder volume after the compression. Internal combustion engines with external ignition, in particular gasoline engines which have a fixed compression ratio only allow to select the compression ratio up to a certain number so that so called knocking under full load of the internal combustion engine is avoided.
However, for the partial load range of the internal combustion engine, thus at a lower degree of filling of the cylinders the compression ratio can be selected with higher values without incurring “knocking”. The important partial load range of an internal combustion engine can be improved when the compression ratio is variably adjustable. Systems with variable piston rod length are known for example for adjusting the compression ratio.
A piston rod is known for example from DE 10 2005 055 199 A1 in which a pivotable lever is inserted into the small piston eye wherein an eccentrical element is inserted into a central opening of the pivotable lever. The eccentrical element is configured to receive a piston pin. The lever forms a shaft—hub connection with the eccentrical element. Since the connection is highly loaded during operation of the piston rod requirements with respect to manufacturing tolerances of the connected elements are high. The support rods supported at an upper piston rod bearing eye are supported with a ball bearing in ball head receivers and bolted down at this location with transversal bolts.